Chapter 20, Problem 20.1P

Interpretation Introduction

To determine:

The electron configuration of ${\text{Co}}^{2+}$.

Concept introduction:

• Electronic configuration of an atom shows how electrons are placed in the orbitals in order of increasing energy.
• The filling of the sublevels progresses in order up to Period 4. However, in the sublevel blocks in Period 4 the 4s sublevel fills before the 3dsublevel.This occurs because the electrons in the 4ssublevel have slightly lower energy than the electrons in the 3d sublevel. This series of 10 elements is called the first transition series (3d).
• 3d elements show large variation in their oxidation states.

Answer to Problem 20.1P

Solution:${\text{Co}}^{2+}$

: $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^7$

Explanation of Solution

Atomic number of cobalt is 27. Thus, it has 27 electrons in its elemental state.

The arrangement of atomic orbitals in increasing order of their energies is as follows:

$1s2s2p3s3p4s3d$

The maximum occupancy of electrons for $s,p,\text{and}d$orbitals is 2, 6, and 10 respectively.

Thus, electronic configuration will be:

$1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^7$

${\text{Co}}^{2+}$has 2 electrons less than that in its elemental state, thus it has 25 electrons.

Now, electrons are first removed from $4s^2$orbitals.

Thus, the electronic configuration of ${\text{Co}}^{2+}$will be:

$1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^7$

(c)

Interpretation Introduction

To determine:

The electron configuration of metal in ${\text{MnO}}_{\text{2}}$.

Concept introduction:

• Electronic configuration of an atom shows how electrons are placed in the orbitals in order of increasing energy.
• The filling of the sublevels progresses in order up to Period 4. However, in the sublevel blocks in Period 4 the 4s sublevel fills before the 3dsublevel.This occurs because the electrons in the 4ssublevel have slightly lower energy than the electrons in the 3d sublevel. This series of 10 elements is called the first transition series (3d).
• 3d elements show large variation in their oxidation states.

Answer to Problem 20.1P

Solution:${\text{MnO}}_{\text{2}}$

: $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^3$

Explanation of Solution

Atomic number of manganese is 25. Thus, it has 25 electrons in its elemental state. The arrangement of atomic orbitals in increasing order of their energies is as follows:

$1s2s2p3s3p4s3d$

The electronic configuration will be:

$1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}3d^5$

Oxygen has an oxidation state of -2, thus in ${\text{MnO}}_{\text{2}}$, 2 oxygen atoms have -4 charge on them. Since molecule is neutral, $Mn$must have an atomic charge of +4. Thus, it has 4 electrons less than that in its elemental state, thus it has 21 electrons. The electrons are first removed from 4s orbital as follows:

$1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^3$

(d)

Interpretation Introduction

To determine:

The electron configuration of metal in ${\text{CuCl}}_4^{2-}$.

Concept introduction:

• Electronic configuration of an atom shows how electrons are placed in the orbitals in order of increasing energy.
• The filling of the sublevels progresses in order up to Period 4. However, in the sublevel blocks in Period 4 the 4s sublevel fills before the 3dsublevel.This occurs because the electrons in the 4ssublevel have slightly lower energy than the electrons in the 3d sublevel. This series of 10 elements is called the first transition series (3d).
• 3d elements show large variation in their oxidation states.

Answer to Problem 20.1P

Solution:${\text{CuCl}}_4^{2-}$: $1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^9$

Explanation of Solution

Atomic number of copper is 29. Thus, it has 29 electrons in its elemental state. The arrangement of atomic orbitals in increasing order of their energies is as follows:

$1s2s2p3s3p4s3d$

The maximum occupancy of electrons for $s,p,\text{and}d$orbitals is 2, 6, and 10 respectively.

Thus, the electronic configuration will be:

$1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{1}3d^{10}$

This is because half filled, and full filled orbitals are more stable.

Chlorine has an oxidation state of -1, thus in ${\text{CuCl}}_4^{2-}$, 4 chlorine atoms have -4 charge on them. Since molecule has a charge of -2, $\text{Cu}$must have an atomic charge of $-(-4-(-2))=+2$. Thus, it has 2 electrons less than that in its elemental state, thus it has 27 electrons.

Now filling up 27 electrons of ${\text{Cu}}^{2+}$

to get its electronic configuration:

$1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}3d^9$